1. Field of the Invention
The present invention relates to a dry etching method, and particularly to a dry etching method for accurate anisotropic etching of aluminum or its alloys at high speeds.
2. Description of the Prior Art
Aluminum or its alloys that form electrodes and wirings of semiconductor integrated circuits are dry-etched by using, as an etching gas, a gaseous mixture of boron trichloride (hereinafter referred to as BCl.sub.3), chlorine (hereinafter referred to as Cl.sub.2), methyl trichloride (hereinafter referred to as CHCl.sub.3) and helium (hereinafter referred to as He) as disclosed in, for example, R. H. Bruce et al., J. Electrochem. Soc., Vol. 130, No. 6, pp. 1369-1372 (1983.6), or by using a gaseous mixture of BCl.sub.3, Cl.sub.2, silicon tetrachloride (hereinafter referred to as SiCl.sub.4) and He as disclosed in R. F. Reicheldefer, Solid State Technology, Vol. 15, No. 6, pp. 64-75 (1982.6)
When aluminum or its alloys are dry-etched using, as an etching gas, the gaseous mixture of BCl.sub.3, Cl.sub.2, CHCl.sub.3 and He, or that of BCl.sub.3, Cl.sub.2, SiCl.sub.4 and He, the etching can be accomplished at a high speed and anisotropically free from undercutting. To accomplish the anisotropic etching at a high speed, however, the RF power density (RF power divided by electrode area, the unit being in W/cm.sup.2) must be maintained at as high as, for instance, 1.8 W/cm.sub.2 when the mixture of BCl.sub.3, Cl.sub.2, CHCl.sub.3 and He is used as an etching gas, or 2.2 to 3 W/cm2 when the mixture of BCl.sub.3, Cl.sub.2, SiCl.sub.4 and He is used as an etching gas. Therefore, when anisotropically etching aluminum or its alloys at high speeds using, as an etching gas, the gaseous mixture of BCl.sub.3, Cl.sub.2, CHCl.sub.3 and He, or that of BCl.sub.3, Cl.sub.2, SiCl.sub.4 and He, the capacity of the RF power source must be increased, and photoresist applied onto the surface of a semiconductor substrate to be etched, is liable to be damaged and thus an anisotropic etching with a small line-width loss, i.e., an accurate anisotropic etching, will not be readily accomplished.